Usability is the measure of the quality of a user's experience when interacting with a product or system — whether a web site, a software application, mobile technology, or any user-operated device.

Usability engineering is a methodical approach to producing a Web site or any user interface. It is a practical and systematic way to deliver a product that works for users. Usability engineering involves several methods, each applied at appropriate times, including gathering requirements, developing and testing prototypes, evaluating design alternatives, analyzing usability problems, proposing solutions, and testing a site or other interface with users.